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3 Introduction Purpose Designing and testing reed relays for switching and carrying high frequency (RF) signals and fast digital pulses Objectives Show how geometrics directly determines a good RF relay The importance of the physical layout of test fixtures determines the test results We will show that the RF signals are directly affected by the conductor materials and material existing between the signal path and the relay shielding

4 Characteristic Impedance Characteristic impedance (Z) can best be used to measure the results of the reed relay s geometry and their material makeup For best RF performance the characteristic impedance must be consistent along the entire signal path Most RF circuits today are 50 Ohms (Ω)

5 Characteristic Impedance How to calculate characteristic impedance The characteristic impedance is a vector and is composed of 3 components: 1. Pure resistance of the circuit 2. The capacitive reactance 3. The inductive reactance

6 Characteristic Impedance The characteristic impedance is given by the following equation: Z = (R 2 + (XL - Xc) 2 ) Here: XL = 2πƒL Xc = 1/(2πƒC) Where: XL is the inductive reactance in Ω Xc is the capacitive reactance in Ω R is the DC resistance in Ω Z is the impedance in Ω ƒ is the frequency L is the Inductance C is the capacitance

7 Characteristic Impedance The calculation for Capacitance and inductance are: C = e A d L = µonda1 2 C is the capacitance Here: C = e A/d L = µonda1 2 Where: L is the inductance e is the permittivity or dielectric constant A is the area of shield and blades d is distance between the plates µo is the permeability constant n is the number of turns d is the length of the signal line A1 is the area of the signal line/shield

8 Characteristic Impedance RF looks at the distributed impedance along the signal path Any changes in impedance will reflect part of its signal backwards This results in an actual loss in signal strength

9 Characteristic Impedance The entire signal path length is critical The impedance is measured from the signal path to the shield The shield is the ground part of the signal path The signal path, the shield and the material between them make up the impedance

11 Characteristic Impedance We will now show you how to calculate the characteristic impedance taking in the different geometries of the reed relay Calculation of the flattened section of reed blade Calculation of the circular section of the reed blade Calculation of the flattened leads as they exit the relay and as they are mounted on a substrate.

12 RF Continuous Wave Parameters Here: Where: Characteristic Impedance Z = 60/( (e)) ln((d)/a) Z is the impedance in Ω e is the dielectric constant D is the diameter of the shield A Is the cross sectional area of the reed blade In is the natural logarithm Flat Reed Switch Blade Diameter (D) Reed Blade (A) Dielectric Shield

17 Testing the Relay We design the relay for RF up to, through and out the package where the leads come out How the leads on connected to our customer s circuit is critical At the junction of our relay and the customer RF circuit (normally to a PCB) the customer must match the impedance of the relay to their circuit

18 Testing the Relay If the customer does not properly match the impedances, the RF characteristics can fall off dramatically This impedance matching requires a knowledgeable RF engineer that can add inductance or capacitance to the junction of the relay/pcb

19 Testing the Relay When we test our relays for RF characteristics, we make up special RF fixtures for testing the relay We also make up special calibration fixtures that compensate for impedance mismatching at the junction of the relay to the PCB

20 RF Testing All the testing information can be shared with our customers The network analyzer information can also be shared electronically with our customers.

22 Ways to Improve RF Performance Shortening the signal path length by making a smaller relay (length wise) LP Series Reed Relay Signal Path going from A to B PCB A B

23 Shortening the Signal Path SIL Series Reed Relay Signal Path going from A to B PCB A B MS Series Reed Relay Signal Path going from A to B is shorter than the SIL Relay PCB A B

24 Shortening the Signal Path CRF Series Reed Relay Signal Path going from A to B showing a dramatic reduction in signal path eliminating the double length of going through the PCB A B PCB

25 Shortening the Signal Path An example of how the RM Series eliminates signal path CRF Series Reed Relays mounted in series Signal Path length A B PCB RM Series 6-Pole Reed Relay Signal Path going from A to B eliminating the path length down and then back up the side of two relays PCB A B

26 Improving Isolation Using higher AT switches works to a limit, where the sacrifice of increased coil power becomes too big a drain

27 Improving Isolation Using a T or 1/2 T switching arrangement will increase isolation 1/2 T Switching Signal in Signal out Signal in Signal out Full T Switching Signal in Signal out Signal in Signal out

28 RF Parameters - Isolation As can be seen the ½ T and T switching will improve the isolation, but the path length has increased So the insertion loss and frequency response will suffer

29 Relays for RF Applications Below is a list of the Standex-Meder RF series and their frequency range RF Relay Series LP Series SIL Series MS Series CR Series Frequency Range DC to 500 MHz DC to 800 MHz DC to 1.5 GHz DC to 7 GHz

32 Summary Reed Relays are excellent RF switching components The Reed Relay RF design is most dependent on its geometric and the material makeup Customer impedance matching entering and exiting the relay is critical for maintaining the 50Ω RF path.

33 PARTNER SOLVE DELIVER For more information on our capabilities, and how we can partner, solve, and deliver to your needs, please visit us at

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